Allan Poe, Van Gogh, Melville, Plath: "I'm interested in glory, and glory is posthumous." Some of the greatest names in the arts were unknown in their lifetimes. It offers hope that genius is bound to triumph in the end to many. But to others, it asks a crucial question: why do we make the hardships of living and an often tragic death such an essential quality in these artists' works to begin with? Emily Bobrow examines.